Small intestinal and colonic changes induced by a chemically defined diet

Growth and Clinical Variables in Nitrogen-Restricted Piglets Fed an Adjusted Essential Amino Acid Mix: Effects of Free Amino Acid-Based Diets

Background

Excess protein intake in early life has been linked to obesity and metabolic syndrome in later life. Yet protein, and in particular the essential amino acids (EAAs), need to be present in adequate quantity to support growth.

Objective

With the use of a piglet model restricted in dietary amino acids (AAs), we compared the efficacy and safety of a standard formula with a low-AA formula containing an adjusted AA composition.

Methods

Female piglets (3-7 d old; Landrace × Yorkshire × Duroc) were fed 1 of 4 isoenergetic AA-based formulas for 14 d (700 kJ · kg body weight-1 · d-1). The formulas contained a set control amount (44 g/L) and AA compositions referred to as the experimental standard (ST-100, n = 22), or 20% or 50% lower total AAs (respectively, ST-80, n = 19 and ST-50, n = 13), or 20% lower total AAs with an optimally adjusted EAA composition (O-80, n = 17). A series of clinical and paraclinical endpoints were measured.

Results

Growth rates were similar for ST-100, O-80 and ST-80 piglets (all ∼15 g · kg-1 · d-1), whereas ST-50 had a markedly lower weight gain relative to all groups (all P < 0.05). Relative to ST-100, all groups with reduced AA intake showed ∼16% reduction in plasma albumin and ∼30% reduction in plasma urea (both P < 0.05). The absolute leucine oxidation rate was ∼30% lower for O-80 than for ST-100 piglets (P < 0.05).

Conclusions

These data show that a 20% reduction in total AA intake for both the control (ST-80) and the adjusted AA (O-80) formula did not have any short-term adverse effects on growth in artificially reared, AA-restricted piglets. The lower absolute leucine oxidation rate observed in O-80 supports the development of an infant formula with an improved AA composition and a moderate reduction in total protein to support adequate growth in healthy infants.

Development of the infant intestine: implications for nutrition support

The incidence of preterm births has continued to increase over the past 25 years, and therefore the optimal feeding of these infants is an important clinical concern. This review focuses on intestinal development and physiology, with a particular emphasis on developmentally immature functions of the preterm intestine and the resulting implications for nutrition therapies used to feed the preterm infant.

New lipids in enteral feeding

PURPOSE OF REVIEW

Lipid sources for enteral nutrition continue to be an exciting area of investigation. It is timely to review recent developments which have largely contributed to thrust enteral feeding into a new era.

RECENT FINDINGS

Although much more research needs to be done, there is a better understanding of the competitive relationships between n-6/n-3 fatty acids in conditions of metabolic and immune stress as well as in autoimmune and degenerative diseases. Although structured lipids are more completely absorbed and cleared, other more important clinical benefits need to be documented before they can be considered cost-effective. Immune enhancing formulas are the subject of controversy and some have been shown to be more effective than others. Enteral formulations with short-chain fatty acids are promising but more experimental work on the normal, and the sick colon is needed. Finally, there are a few isolated studies suggesting that enteral feeding with liposomes and with lipolytic products may have advantages when the digestive phase needs to be circumvented. The era of nutrigenomics, in which the effect of specific lipids on genes and proteins is being explored, is with us. We can look forward to nutrigenetics when the effect of genetic variation on the interaction between diet and disease will guide our practice.

SUMMARY

Clinicians already have access to lipid sources and formulations which allow them to individualize enteral feeding programs. More clinical and technological research needs to be carried out, however, before products can be tailored to produce optimal effects in specific conditions.

Adaptation following intestinal resection: mechanisms and signals

The intestine has an inherent ability to adapt morphologically and functionally in response to internal and external environmental changes. The functional adaptations encompass modifications of the brush border membrane fluidity and permeability, as well as up- or down-regulation of carrier-mediated transport. Intestinal adaptation improves the nutritional status following the loss of a major portion of the small intestine, following chronic ingestion of ethanol, following sublethal doses of abdominal irradiation, in diabetes, in pregnancy and lactation, with ageing, and with fasting and malnutrition. Following intestinal resection, morphological and functional changes occur depending upon the extent of the intestine removed, the site studied, and the lipid content of the diet. Therefore, intestinal adaptation has important implications in the survival potential and welfare of the host. An understanding of the mechanisms of, and signals for, intestinal adaptation in the experimental setting forms the basis for the use of management strategies in humans with the short-bowel syndrome.

Key nutrients and growth factors for the neonatal gastrointestinal tract

The nutritional support of gastrointestinal growth and function is an important consideration in the clinical care of neonatal infants. In most health infants, the provision of either breast milk or formula seems to support normal intestinal mucosal growth, but the most significant advantages of breast milk may be for host defense or gut barrier-related functions that are involved in reducing infection. The specific effects of various milk-borne growth factors on key mucosal immune and barrier functions are likely to provide valuable new clues to the advantages of human milk. A substantial number of preterm, low-birth weight babies or those suffering from compromised intestinal function, however, often cannot tolerate oral feedings and instead receive TPN. The consequences of TPN on gastrointestinal function and how this contributes to morbidity of these infants warrants further study, with respect to both clinical and basic research questions. Although enteral nutrition seems to be a critical stimulus for intestinal function, the minimal amounts and composition of nutrients necessary to maintain specific intestinal functions remain to be established. The experimental tools exist to start defining the specific nutrient requirements for the infant gut and some of these nutrients are known (e.g., glutamate, glutamine, and threonine). Peptide growth factors and gut hormones clearly play a role in gut growth and in several ways mediate the trophic actions of enteral nutrition. Although a number of these growth factors are good candidates for therapeutic use, their clinical application in the management of gastrointestinal insufficiency and disease has been slow. The emergence of GLP-2 as a trophic peptide that seems to target the gut is a promising candidate on the horizon.

Dietary lipid composition modifies intestinal morphology and nutrient transport in young rats

BACKGROUND

Varying lipid content of the diet of pregnant and nursing dams results in alterations in sugar and lipid uptake into the intestine of their suckling offspring. In this study, we wished to determine whether the same alterations in dietary lipid result in adaptation of intestinal transport in postweaning rats.

METHODS

During nursing, the dams were fed the same diet that their offspring were fed for 3 more weeks after weaning. These semipurified diets contained: 1) 15.8% of total fatty acids (w/w) as 18:2n-6 and an n6/n3 ratio of 7.3:1; 2) a diet with 17.6% of total fatty acids as 18:2n-6 and an n6/n3 ratio of 4:1; 3) a diet with 16.2% of total fatty acids as 18:2n-6 and 1.2% arachidonic acid (AA); 4) a diet with 16.8% of total fatty acids at 18:2n-6, 1.2% AA and 0.7% docosahexaenoic acid (DHA); and 5) a diet with 16.0% of total fatty acids as 18:2n-6 and 0.7% as DHA. The in vitro uptake of D-glucose, D-fructose, medium- or long-chain fatty acids and cholesterol was assessed in 6-week-old rats.

RESULTS

Feeding AA increased the Vmax for jejunal and ileal uptake of glucose, compared with the high n6/n3 diet. This effect was prevented by adding DHA to the AA diet. The low n6/n3 fatty acid ratio diet decreased uptake of fructose as compared with the high n6/n3 diet, and the increased uptake of fructose with DHA was prevented by adding AA. The incremental change in free energy associated with uptake of medium chain-length fatty acids was lower in the jejunum of animals fed AA plus DHA as compared with the other diet groups. Jejunal uptake of 18:0 was lower for animals fed DHA or AA plus DHA, as compared with AA alone; ileal rate of uptake of long-chain fatty acids was unaffected by diet.

CONCLUSIONS

The intestine of young rats modifies its intestinal morphology and adapts its nutrient transport in response to variations in dietary lipids. In postweaning rats, the potentially undesirable effect of one fatty acid on nutrient uptake may be countered by adding a select second fatty acid to the diet.

Nutritional support in malnourished paediatric patients

An imbalance between a person's energy requirements and his or her dietary protein and caloric supply is the source of protein energy malnutrition (PEM), which compounds the problems of any underlying disease. Malnutrition may occur quite rapidly in critically ill patients, particularly those suffering from sepsis, setting up a vicious cycle with worsening of the PEM. This chapter examines the main consequences of PEM, the means whereby appropriate nutrition may be provided, and risks for severely malnourished paediatric patients in hospital. If the gastrointestinal tract can be used for refeeding, it should be used. When the gastrointestinal tract is unable to meet the protein and energy requirements, parenteral nutrition (PN) is required. PN is efficient but carries a high risk of metabolic complications known as the refeeding syndrome and directly related to the homeostatic changes secondary to severe PEM. Catch-up growth may be achieved by using appropriate nutritional support. Changes in body composition have to be assessed during the course of renutrition.

Inhibition of lipid absorption as an approach to the treatment of obesity

A reduction in fat intake may be achieved by making educated choices to reduce total calorie intake, to consume a lower quantity of total fats, or to modify the ratio of saturated-to-polyunsaturated lipids. Leptin agonists or NPY or CCK antagonists may prove to be useful to diminish appetite and thereby reduce the total intake of food. But eating has such cultural, social, and hedonistic attributes that such a single-pronged approach is unlikely to be successful. The use of fat substitutes may prove to be popular to provide a wide range of snack food options, but these are likely to be of minimal use in weight reduction programs because of their distribution of additives in only a limited number of foods. The inhibitors of lipid digestion will be modestly successful in the short term; their long-term success will be influenced by gastrointestinal adverse effects and the need to consume fat-soluble vitamin supplements to prevent the development of fat-soluble vitamin deficiencies. The inhibition of lipid absorption is an attractive targeted approach for the treatment of obesity, since this would reduce the uptake of visible as well as invisible fats, which would potentially offer convenient dosing, and could also be a means to inhibit secondarily the uptake of carbohydrate calories.

Caloric restriction increases the expression of heat shock protein in the gut

OBJECTIVE

The authors determined whether caloric restriction (CR) either acutely or chronically, alters heat shock protein 70 (hsp70) gene expression in the gut.

SUMMARY BACKGROUND DATA

Caloric restriction prolongs the life span and delays age-related disease (e.g., cancer) in mammals; the mechanisms responsible for these effects are not known. Heat shock proteins are a group of stress-responsive genes of which the most prominent member is hsp70.

METHODS

In the first experiment, adult (4-month-old) rats (n = 3/group) were killed after a 48-hour fast or 6 and 24 hours after refeeding. In addition, three rats (controls) were killed without fasting or refeeding. The stomach was removed and RNA was extracted for hsp70 gene expression. In the second experiment, aged (22- to 26-month-old) rats were fed ad libitum (AL) or a CR diet (60% caloric intake of AL diet). Rats were killed, the stomach and duodenum were removed, and RNA was extracted for determination of hsp70 gene expression.

RESULTS

In the first experiment, hsp70 mRNA levels were increased approximately threefold in the stomach of rats fasted for 48 hours; levels decreased to control values by 6 and 24 hours after refeeding. In the second experiment, hsp70 mRNA levels were increased significantly in both the stomach and duodenum of aged CR rats compared with AL controls.

CONCLUSIONS

The authors have demonstrated that hsp70 mRNA levels are increased in the proximal gut of young and old rats, either acutely (with fasting) or with CR. Increased expression of the cytoprotective hsp70 gene in the gut may provide a possible cellular mechanism for the beneficial effects noted with CR.

Econutrition and health maintenance — A new concept to prevent GI inflammation, ulceration and sepsis

The nutritional needs of the gastrointestinal mucosa per se has until today been largely neglected. It is a rather novel finding, that the lower part of the digestive tract is most dependent on luminal nutrition for maintaining its integrity, structure and function. Even the most complete parenteral nutrition (PN) regimen cannot, in the absence of adequate enteral nutrition (EN), fully prevent the development of mucosal atrophy in the lower part of the digestive tract, especially the colon. Nor can PN prevent the downregulation of the colon's many important functions. Increased microbial translocation and a predisposition to sepsis are consequences of inadequate luminal nutrition. Such developments can only be prevented by oral feeding and the local 'manufacturing' of essential nutrients in the colon. Probiotic bacteria are also important, especially with respect to the function of the colonic mucosa, which is the focus of this review.

Gastrointestinal growth in rats as influenced by indigestible polysaccharides and adaptation period

Hypertrophy of the small intestinal tissue evolved during the initial 9 days in rats fed pectin or guar gum. Hypertrophy of the caecal and colonic tissue continued beyond day 9. Caecal hypertrophy was observed in rats fed pectin, guar gum or resistant starch, while colonic hypertrophy was observed only in rats fed pectin or resistant starch. There is a time lag in the adaptive response of the caecum and colon as compared with the small intestine, at least for dietary polysaccharides. This time lag is suggested to be related to the time required for the microflora to adapt to the dietary PS.

Effect of fiber and its fermentation on colonic adaptation after cecal resection in the rat

BACKGROUND

The role of fiber in postresection adaptation is poorly understood. We examined the significance of short-chain fatty acids produced by intracolonic fiber fermentation during colonic adaptation.

METHODS

Rats underwent one of three surgeries: control laparotomy, cecal resection, or cecal resection with placement of perfusion catheter. Rats of each surgical group were randomly assigned to receive treatment regimens of standard fiber diet (with or without fermentation-suppressing antibiotics), fiber-free diet, or diet plus intracolonic perfusion of short-chain fatty acids. Adaptation parameters of mucosal weight, mucosal DNA and protein content, water absorption, and butyrate absorption were measured.

RESULTS

Compared with controls, postresection rats that were fed fiber had 65% greater basal and 112% greater butyrate-stimulated water absorption as well as 140% greater butyrate absorption. Fiber-fed rats exhibited significantly greater colonic weight and colonic mucosal protein after cecal resection. These changes were absent in postresection rats fed a fiber-free diet. Inhibition of fermentation by neomycin and metronidazole added to a standard fiber diet also prevented postresection adaptation. All adaptive changes were restored when the cecal-resection rats that were fed the fiber diet with antibiotics received an intracolonic infusion of short-chain fatty acids. Adaptation did not occur when short-chain fatty acids were infused into colons of postresection rats that were fed a fiber-free diet.

CONCLUSIONS

Cecal resection leads to significant functional and structural changes in the adapting residual colon. Fermentation of dietary fiber by colonic flora to short-chain fatty acids is necessary, but it alone is not sufficient to mediate adaptation.

Effects of diet on experimentally induced intestinal ulcers in rats: morphology and tissue leukotrienes

The effects of dietary pretreatment on longitudinal ulcers of the intestine induced by indomethacin given intracolonically were investigated in rats. The rats were pretreated with either standard diet or liquid meals. Intracolonic indomethacin (24 mg/kg/day) given for two days produced longitudinal ulcers and small scattered ulcers in the small intestine in the control rats that were receiving standard pelleted formula. Three days pretreatment with one of two types of liquid meals, low residual diet (LRD) or elemental diet (ED), significantly reduced the incidence (3% in ED group and 0% in the LRD group) and the length of the longitudinal ulcers in the small intestine. The caecum was affected in each dietary pretreatment group (67% in controls, 80% in LRD group, and 69% in ED group). Colonic ulcers that were located in a longitudinal fashion were found in 42% of LRD group, while these ulcers were less frequently found in the ED group (13%) and controls (0%). Development of ulcers in the caecum and in the colon of rats in ED and LRD groups was more delayed than that of small intestinal ulcers of control rats. In another experiment, pretreatment by ED significantly increased colonic tissue leukotriene B4 concentration when compared with that of controls. These findings suggest that the site of experimental enteropathy induced by indomethacin given intracolonically can be modified by dietary pretreatment. This animal model can be available for investigating differences in the pathophysiology of enteropathy according to the site of involvement.

Alteration of mucosal immunity after long-term ingestion of an elemental diet in rats

The effects of an elemental diet on lymphocyte transport in intestinal lymph and immune responses of gut-associated lymphoid tissue were investigated in rats. The control animals were fed a conventional diet. After 4 week of feeding, the total calorie intake and body weight gain showed no differences between the two groups. The number and total area of Peyer's patches and the ratio of height of villi to height of crypt showed no significant differences between the two groups. The rate of lymph flow in intestinal lymphatics showed no significant change in treated animals compared with the control rats. However, an elemental diet induced a significant decrease in lymphocyte flux in intestinal lymphatics compared with that in control rats. Lymphocyte subsets in intestinal lymph revealed a significant decrease in CD3-positive cells, especially CD4-positive cells in the elemental diet-treated group. A significant decrease in the number of immunoglobulin A-containing cells and a decreased CD4/CD8 ratio in T-cell subsets were observed in the lamina propria of ileal mucosa in the elemental diet-treated group by morphometric analysis in the immunohistochemical study. Specific antibody-secreting cells in intestinal lymph were also investigated after rats were intraduodenally primed with cholera toxin and challenged with the same toxin after an interval of 2 weeks. No significant difference was seen between the two groups in any of the numbers of anti-cholera toxin immunoglobulin-secreting cells in any immunoglobulin A, immunoglobulin G, or immunoglobulin M class as determined by the enzyme-linked immunospot assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetic studies on the metabolism of short-chain fatty acids and glucose by isolated rat colonocytes

BACKGROUND/AIMS

Although the interest in colonic mucosal metabolism of short-chain fatty acids is steadily increasing, the kinetic parameters Vmax (maximum velocity) and Km (Michaelis constant) of the complete oxidation of these acids into CO2 by colonic epithelial cells have not previously been determined.

METHODS

Isolated rat colonocytes were incubated in the presence of a concentration range of 14C-labeled acetate, propionate, butyrate, and glucose. Oxidation rates were obtained by quantifying the production of 14CO2. Vmax and Km were calculated by computer-fitting of the data to a Michaelis-Menten plot.

RESULTS

The apparent Vmax values were similar comparing acetate, propionate, and butyrate (1.114 +/- 0.061, 0.991 +/- 0.072, and 1.007 +/- 0.070 mumol/min.g, respectively), but significantly lower for glucose (0.339 +/- 0.022 mumol/min.g). The corresponding Km values were all different and in the order of butyrate (0.184 +/- 0.017 mmol/L) < propionate (0.339 +/- 0.025 mmol/L) < acetate (0.487 +/- 0.019 mmol/L) < glucose (0.777 +/- 0.051 mmol/L). In substrate competition experiments, butyrate caused a strong noncompetitive inhibition of acetate oxidation and a mixed type of inhibition of propionate oxidation. Propionate inhibited the oxidation of acetate noncompetitively and that of butyrate competitively. Acetate only slightly inhibited the oxidation of propionate and butyrate.

CONCLUSIONS

Colonic epithelial cells seem to utilize short-chain fatty acids in a preferential order of butyrate > propionate > acetate. Oxidation of propionate or acetate, however, may provide the energy needed for cellular functions if the metabolism of butyrate is impaired or the luminal supply is limited.

Selective bowel decontamination, nutritional therapy and bacterial translocation after burn injury

We studied the influence of selective bowel decontamination (SBD) with neomycin, on bacterial translocation (BT) in rats treated with early post-burn parenteral nutrition (TPN) or enteral nutrition (TEN). Male Wistar rats were randomly assigned to receive either TPN (groups 1, 2) or an isonitrogenous, isocaloric polymeric diet (TEN, groups 3, 4) or a standard rat chow ad libitum (group 5), for 5 days after burn injury (30% b. s. area). In addition, groups 1 and 3 received a daily oral dose of neomycin (30 mg/kg) during the same period. At the end of the study, animals were killed and the mesenteric lymph nodes (MLN), liver (L) and spleen (S) were removed for microbiological cultures. The overall incidence of BT was MLN: 67%, L: 58% and S: 42% with a mortality rate of 12.2% In MLN and L, group 5 showed significantly less BT than groups 1 and 2 (30% vs 84%, p < 0.02) and groups 3 and 4 (38% vs 76%, p < 0.05), respectively. No differences were found between TPN and TEN groups. SBD (groups 1 and 3) resulted in a significantly lower mortality rate (26% vs 0%, p < 0.05) and BT in the liver (38% vs 100%, p < 0.001) than rats without antibiotic treatment (groups 2 and 4). It is concluded that early post-injury TPN or TEN promote BT to a greater extent than a standard chow. In addition, SBD with neomycin prevents mortality and BT after burn injury.

The effect of total parenteral nutrition on gastrointestinal hormones in rats

Total parenteral nutrition (TPN) has been shown to alter the serum concentration of certain gastrointestinal hormones. However, the effects of surgical and nutritional techniques have not been evaluated adequately. This study examined the effects of those techniques on serum gastrin and secretin levels in Fischer 344 rats fed TPN. After aseptic superior vena cava cannulation and a 4-day postoperative recovery period with ad libitum access to food and water, 18 rats were randomly and equally (n = 6) assigned to either (1) a baseline group, killed after the recovery period; (2) a TPN group fed sufficient nutrients (67% dextrose, 21.7% amino acid, 11.3% fat) and kilocalories (1.45 kcal/mL) for normal growth and development; or (3) an orally fed (OF) group fed ad libitum a powdered diet isocaloric and isonitrogenous to the TPN solution. Both the TPN and OF groups were fed for 5 days and then killed. Another set of six rats without surgery served as a control (CON) group and had the same diet protocol as the OF group. Serum was analyzed for gastrin and secretin by radioimmunoassay. The OF group had significantly (p < .01) lower gastrin levels than the CON group. Gastrin levels of OF rats were twofold lower (p < .04) than those of the TPN rats and were threefold greater (p < .02) than those of the baseline group. Secretin levels in OF rats were twice as high (p < .02) as those in CON rats. The OF group showed a trend toward significantly (p < .09) higher serum secretin levels when compared with the TPN group.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of enteral feeding on intestinal epithelial proliferation and fecal bile acid profiles in the rat

The preservation of colonic mucosal mass requires the presence of feces; thus, colonic hypoplasia develops with enteral feeding. Fermentable soy fiber may maintain fecal bulk and prevent mucosal atrophy. We therefore compared the effects of Enrich (containing soy fiber) with Ensure (fiber-free) on mucosal mass, fecal bile acids, and cell proliferation in the rat. Sprague-Dawley rats (n = 20) were randomized into groups receiving either standard rat food, Enrich, or Ensure. After 4 weeks, rats were weighed and killed at intervals after administration of vincristine sulfate (1 mg/kg intraperitoneally), which was given to induce metaphase arrest within the intestinal crypts and to allow calculation of crypt cell production rate. Fecal free bile acids and neutral steroids were analyzed using gas-liquid chromatography and gas-liquid chromatography mass spectrometry. Nucleic acid concentrations in the small and large intestine and crypt cell production rate in the small bowel were unaffected by diet. In the proximal large bowel, both enteral diets produced a marked reduction in crypt cell production rate to values only 5% to 7.5% of control values (p < .001). In the midcolon of rats fed Ensure, there was a similar reduction, but this hypoplastic effect was completely prevented by Enrich. Without an elevation in the lithocolic acid to deoxycholic acid ratio, secondary bile acid concentrations were increased in rats receiving Enrich (p < .05 to .01) but not in those receiving Ensure. Thus, fermentable soy fiber diets may prevent the midcolonic mucosal hypoplasia induced by enteral feeding.

Effect of luminal growth factor preservation on intestinal growth

Intestinal atrophy contributes to the clinical difficulties of patients who cannot eat normally. Atrophy is prevented by luminal food proteins but not by the equivalent aminoacids. This observation is not explained by current theories of intestinal physiology. Epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) are secreted into the gut lumen. We speculated that these are digested by pancreatic enzymes in fasting juice, but preserved when food proteins block the active sites of these enzymes. Studies based on molecular size and bioactivity confirmed that fasting human jejunal juice destroys EGF and TGF alpha. EGF, but not TGF alpha, was preserved when the milk protein casein or an enzyme inhibitor were present; elemental diets were ineffective. Diversion of pancreatic juice to the mid point of the small intestine in rats significantly increased luminal EGF-like bioactivity and all variables of growth in the proximal enzyme-free segment. Our findings support a novel mechanism of control of intestinal growth, which has important clinical implications. The addition of enzyme-inhibiting proteins such as casein to elemental diets may preserve intestinal integrity and function.

Trophic effects of different enteral diets in the rat intestine

The trophic effect of 4 commercial diets compared to chow was studied in 50 rats. The 4 commercial diets were: a free amino acid diet, a diet based on soy protein hydrolysate and two diets based on intact protein with and without extra fibre added. Bowel weight, mucosa weight and DNA content were measured after 7 days of treatment. The enteral formula based on a soy protein hydrolysate had a significant growth stimulating effect on the proximal small bowel compared to rat chow. In the ileum and in the colon all diets without fibre supplementation caused significantly lower bowel weights than rat chow.

Neurotensin prevents intestinal mucosal hypoplasia in rats fed an elemental diet

Liquid elemental diets are associated with mucosal hypoplasia of both the small intestine and colon. Neurotensin, a tridecapeptide widely distributed in the gut, is trophic for the small intestine of rats fed a normal chow diet. The purpose of this study was to determine whether neurotensin could reverse the hypoplasia of intestinal mucosa that is associated with feeding a liquid elemental diet. Forty male Sprague-Dawley rats were randomized into five groups. Four groups were fed (for seven days) a glutamine-free liquid elemental diet. Subcutaneous injection of saline (control) or neurotensin (33, 100 or 300 micrograms/kg) were given to the groups of rats every 8 hr for seven days. Group five (Chow) received rat chow ad libitum for seven days. Rats were killed on day 8, and the proximal jejunum, distal ileum, and proximal colon removed. Mucosal weight, DNA, RNA, and protein contents were determined. Neurotensin (300 micrograms/kg) increased the cellularity of the small intestinal mucosa and reversed mucosal hypoplasia due to an elemental diet; a more pronounced effect was noted in the jejunum compared to the ileum. Neurotensin (33 and 100 micrograms/kg) increased mucosal DNA content in the jejunum but was not effective in reversing the hypoplasia. Neurotensin had no effect on growth of colonic mucosa. These results suggest that neurotensin may be an important trophic hormone for the small intestine. Administration of neurotensin may alleviate hypoplasia of the small bowel mucosa and maintain functional integrity of the gut during prolonged feeding of an elemental diet.

Effect of dietary fat on the distribution of mucosal mass and cell proliferation along the small intestine

This study investigated how substitution of long chain triglycerides for glucose in a mixed diet affects the overall small intestinal mucosal mass and the distribution of mucosal mass and cell proliferation along the small intestine. Four groups of eight female Wistar rats (180-200 g) were isocalorically fed mixed diets containing the essential fatty acid rich oil Efamol substituted for glucose at concentrations of 1.2%, 10%, 25%, and 50% total calories for 20 to 23 days. The small intestine was divided into three equal length segments and whole gut weights, mucosal weights, protein and DNA determined. Cell proliferation was estimated from the two hour accumulation of vincristine arrested metaphases in microdissected crypts at points 0%, 17%, 33%, 50%, 66%, and 100% small intestinal length. There were no differences between groups in parameters of overall small intestinal or distal segment mucosal mass. With increasing levels of fat, however, there was a significant trend for the mucosal mass of the proximal segment to fall and that of the middle segment to rise. The pattern of two hour metaphase accumulation reflected these changes. These regional changes in mucosal mass and cell proliferation may reflect differences in the sites of absorption of fat and glucose.

Effect of short-chain fatty acids on colonic function and structure

Short-chain fatty acids (SCFA), fermentation products of fiber, are believed to play a role in intestinal adaptation. Although the administration of fiber or the infusion of SCFA has been shown to cause colonic growth, studies have been done primarily in enterally fed animals. In addition, the effects of SCFA on absorptive function have not been determined. Adult male rats were maintained on total parenteral nutrition (TPN) and, in addition, received either 150 mmol/L of saline or 150 mmol/L of SCFA mixture (60:25:15, acetate:propionate:butyrate) into the proximal colon. One week later, the in vivo absorption of water, electrolytes, and 20 mmol/L of butyrate was measured. After the rats were killed, parameters of colonic mass were determined. SCFA infusion into the colon had no significant effect on absorptive function. However, significantly greater mucosal height (p less than .01) and mucosal DNA (p less than .05), were observed. Although SCFA has a modest effect on colonic structure, they do not influence absorptive function in TPN rats.

Effect of short-chain fatty acids on the human colonic mucosa in vitro

Fermentable dietary fiber components are known to stimulate colonic crypt proliferation. As these compounds are rapidly degraded to short-chain fatty acids (SCFAs) by the anaerobic microflora, the hypothesis was tested that this trophic effect of fiber may be mediated by SCFAs. Biopsies were taken from normal cecal mucosa of 45 individuals during routine colonoscopy. They were incubated for 3 hours with sodium salts of SCFAs at physiological concentrations (three SCFAs = acetate 60 mmol/L + propionate 25 mmol/L + butyrate 10 mmol/L; acetate 60 mmol/L; propionate 25 mmol/L; butyrate 10 mmol/L) or equimolar NaCl (control). Cell proliferation was measured autoradiographically by subsequent pulse labeling with [3H]thymidine (1 hour). The labeling index (number of labeled cells divided by the total number of cells) was computed for the crypt as a whole and for five equal crypt compartments (compartment 1 = crypt base, compartment 5 = crypt surface). Cecal crypt proliferation was raised significantly in all incubation experiments with SCFAs. Butyrate (10 mmol/L, increase + 89%) and propionate (25 mmol/L, + 70%) were as effective in stimulating proliferation as the combination of three SCFAs (+103%), although the effect of acetate (+31%) was minor. Increasing the butyrate concentration to 25 mmol/L or 60 mmol/L did not result in a further increase of cell labeling. SCFAs stimulated proliferation in the basal three crypt compartments only. An expansion of the proliferative zone to compartments 4 and 5 was not observed. SCFAs, especially butyrate and propionate, are luminal trophic factors for the cecal epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)

[What is the role of nutrition in Crohn disease? A contribution to the importance of dietary therapy in regional enteritis]

The clinical appearance of Crohn's disease (CD) is especially marked by nutritional deficits and insufficiencies. For a long time the goal of nutritional care was reduced to the readjustment of the nutritional status. The development and clinical use of controlled parenteral nutrition (TPN) and enteral nutritive solutions (EN) did not only emphasize this therapeutical issue, but furthermore showed positive effects on the conservative as well as on the surgical treatment concepts. Therefore today artificial nutritional support is a firm part of therapy in acute, active phases or in the contact of surgical management of CD. This is especially valid in children, where complications in general and growth failure in particular can be reduced. EN is the preferred feeding method in most of the cases, due to a lower complication rate and reduced cost when compared to TPN. The question regarding the importance of nutritional support as primary therapy has also been investigated. The results differ extensively, but point towards the conclusion that patients with solitary small bowel disease do profit from this therapeutical concept. Nevertheless it is unclear, how TPN or EN interfere in the pathophysiology or -biochemistry in this process. A question about reduction e.g. of allergic components of daily diet did stimulate new theories regarding the hypothesis of a possible causal relationship between diet and the pathogenesis of CD. Investigations on dietary habits and daily dietary therapy did not reveal an overall accepted dietary guideline. Nevertheless it seems obvious that dietary counselling has a positive effect on the disease process. It does appear, that today in the acute, active phase as well as in the long term management of Crohn's disease nutritional-care is an important therapeutical method.

Liver dysfunction in critical illness

Abnormal liver function commonly accompanies critical illness. Ischaemic hepatitis occurs with shock and is characterised by elevated plasma aminotransferase concentrations. 'ICU jaundice' occurs later in critical illness, especially after trauma and sepsis. The major biochemical abnormality is conjugated hyperbilirubinaemia. The clinical setting suggests that hepatic ischaemia and hepatotoxic actions of inflammatory mediators are the major aetiological factors. Massive blood transfusion, effects of nutritional support and drug toxicity may contribute. Both the presence and degree of jaundice are associated with increased mortality in several nonhepatic diseases. It is proposed that Kupffer cell phagocytic depression associated with liver dysfunction permits systemic spread of endotoxin and inflammatory mediators and thus predisposes to multiple organ failure. Immunosuppression, metabolic abnormalities, impaired drug oxidation and myocardial depression may contribute to the poor prognosis. There is no specific treatment, but prompt resuscitation, definitive treatment of sepsis and meticulous supportive care will likely reduce the incidence and severity.

Bacterial overgrowth and intestinal atrophy in the etiology of gut barrier failure in the rat

Bacterial translocation occurs in animal models of shock, trauma, sepsis, and parenteral or elemental enteral alimentation. Bowel atrophy and cecal bacterial overgrowth have both been implicated in the pathophysiology of bacterial translocation in many of these models. To further define the etiology of bacterial translocation resulting from dietary manipulations, rats were fed a elemental/defined-formula diet (DFD) for 2 weeks ad libitum and then randomized to either intestinal decontamination with a nonabsorbable antibiotic (neomycin) or no antibiotic treatment. Neomycin treatment significantly (p less than 0.01) reduced the incidence of bacterial translocation after DFD, in association with a significant reduction in the number of cecal gram-negative bacteria. Neither loss of bowel mass after DFD nor bowel composition was affected by oral neomycin. Bacterial translocation after DFD would thus appear to be the result of cecal bacterial overgrowth rather than a loss of a physical intestinal barrier due to atrophy.

[Dietary fiber. Effect on colon carcinogenesis]

The etiopathogenesis of colon carcinogenesis is supposed to be a two-step process consisting of initiation and promotion. In human nutrition the range of xenobiotics acting possibly as initiators occurs mostly in very low concentrations. Therefore, performing a one-factorial consideration they are not claimed seriously to account for initiation. On the contrary, it can be taken for granted that bile acids exert promoting effects in connection with colon carcinogenesis. All factors influencing the promoting effect of bile acids are able to do so probably due to a decrease of pH and as a result the shift of the two bile acid fractions in favour of the soluble fraction, and/or due to the intensification of shift of bile acid metabolism (7-alpha-dehydroxylase). These processes are indirectly influenced to a large extent by the lipid content of food as a result of cholegenesis induction. The "protective Effect" of dietary fibre in colon carcinogenesis (reduced number of tumour carriers, and/or number of tumors per animal) cannot been interpreted as such. Only a delayed promotion phase could been proven. It can be reached only by plant products (bran, lupin), but not by dietary fibre in general.

Effect of enteral diets on whole body and gut growth in unstressed rats

The composition of enteral feeding formulas may have different effects on total body and gut growth. We studied the growth effects in rats of a complex solid fiber-based diet (Prolab Rodent Diet) with that of three isocaloric and isonitrogenous commercially available liquid feeding formulas which differ in their type of protein (Osmolite HN, an intact protein formula; Reabilan HN, a peptide formula; and Vivonex-TEN, an amino acid formula). Total body weight gain was greatest with the rodent diet (93 +/- 2 g/10 days), followed by the peptide diet (72 +/- 5 g/10 days) and intact protein diet (58 +/- 8 g/10 days). Weight gain was significantly lower on the amino acid diet (43 +/- 7 g/10 days). Proximal and mid gut mass was comparable with all four diets, but distal gut mass was significantly lower with the amino acid diet. Somatomedin C levels on the rodent diet (13.3 +/- 1.8 nM), and the peptide diet (14.0 +/- 3.3 nM) were significantly higher than somatomedin C levels on the amino acid diet (8.0 +/- 1.0 nM). Somatomedin C levels on the intact protein diet (9.6 +/- 1.4 nM) were intermediate between the rodent diet and amino acid diet. We conclude that growth effects vary with different enteral diets (unrelated to total calories and protein) and may result from differences in the generation of tissue growth factors.

The starved colon--diminished mucosal nutrition, diminished absorption, and colitis

Nutrition of colonic epithelial cells is mainly from short chain fatty acids (SCFAs) produced by bacterial fermentation in the colonic lumen. n-Butyrate contributes more carbon of oxidation to epithelial cells than glucose or glutamine from the vasculature. Incomplete starvation of colonic epithelial cells through lack of luminal SCFAs leads, in the short term, to mucosal hypoplasia with either diminished absorption or diarrhea. A chronic lack of SCFAs or complete organ starvation in conjunction with other factors leads to nutritional colitis, either "diversion colitis" or "starvation colitis." Whether predominantly diarrhea or colitis develops in mucosal malnutrition appears to depend upon the severity and duration of starvation. Ulcerative colitis may be classified as a nutritional colitis in that colonic epithelial cells are unable to utilize SCFAs reflecting epithelial starvation despite abundant SCFAs.

Bulk prevents bacterial translocation induced by the oral administration of total parenteral nutrition solution

The effects of a fat and glutamine-free orally administered total parenteral nutrition (TPN) solution on intestinal mucosal mass, morphology, barrier function, and cecal bacterial population levels were measured in CD-1 mice. Ileal mucosal protein content decreased by 63% (p less than 0.01) in the oral TPN-fed mice, although they gained weight on this diet. These TPN-fed mice also exhibited changes in mucosal structure and the normal ecology of their cecal microflora was disrupted leading to overgrowth with Gram-negative enteric bacilli. These changes in intestinal mucosal mass, morphology, and gut bacterial ecology were associated with an increased incidence of bacterial translocation (BT) (TPN group 70% BT vs control group 15% BT: p less than 0.01). The administration of cellulose fiber or kaolin (bulk-forming agents), but not of citrus-pectin (a fully-fermentable, nonresidue fiber) reduced the incidence of BT in the TPN-fed mice to control levels. The beneficial effects of these bulk-forming agents appeared to be due to their ability to prevent TPN-induced disruption of the intestinal microflora and alterations in intestinal morphology, even though they did not prevent ileal mucosal protein levels from decreasing. These results suggest that the administration of bulk forming agents will prevent the loss of intestinal barrier function against luminal bacteria that occurs in mice fed an oral TPN solution.

Stimulation of intestinal mucosal growth with intracolonic infusion of short-chain fatty acids

Dietary fiber, which stimulates intestinal mucosal growth, is fermented by anaerobic bacteria in the rat hindgut to the short-chain fatty acids (SCFA) acetate, propionate, and butyrate. Butyrate is the preferred oxidative fuel of the colonocyte in vitro, and the provision of preferred intestinal fuels has been shown to stimulate mucosal proliferation in vivo. This study determined whether chronic colonic infusion of butyrate or a combination of SCFA would stimulate intestinal mucosal growth in an animal deprived of its normal source of SCFA, fiber fermentation in the cecum. Adult male Sprague-Dawley rats were fed a fat- and fiber-free elemental liquid diet and underwent cecectomy, ileocolic anastomosis, and insertion of a proximal colonic infusion catheter. Rats were then assigned to receive either a continuous infusion of butyrate (20 mM, 40 mM, or 150 mM), SCFA (70 mM acetate + 35 mM propionate + 20 mM butyrate), or saline, or to receive no infusion. A seventh group underwent proximal colonic transection and reanastomosis. After 7 days, jejunal, ileal, and proximal colonic segments were analyzed for mucosal weight, protein, RNA, and DNA. In the colon, the 40-mM butyrate infusion resulted in significant elevations in all mucosal parameters relative to all three control groups, saline infusion, no infusion, and transection. Both the 20-mM butyrate and the SCFA groups showed increased colonic mucosal DNA compared to controls. In the jejunum and ileum, mucosal DNA content was significantly greater in the SCFA group than in the control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in serum levels, anti-tumor activity and toxicity of methotrexate in rats after a short period of nutritional depletion

The alterations in serum levels, anti-tumor activity and host toxicity of methotrexate (MTX) were tested in tumor bearing rats following a period of dietary manipulation. A protein deprived (PD) diet or a diet containing a normal protein content (NP) was administered for 5 days and MTX injected intra-peritoneally (i.p.) at the end of the 5 day period. The MTX serum levels were significantly elevated in rats which received the PD diet, as compared to NP dietary rats. This elevation correlated with an enhanced tumor response to MTX administration. In addition, bone marrow toxicity and intestinal tract toxicity, measured with flow cytometry (FCM) of the bone marrow and morphometry of the jejunal mucosa respectively was increased in rats receiving the PD diet. These results indicate that the serum clearance of MTX is delayed in animals suffering from malnutrition, leading to both enhanced tumor response and increased host toxicity.

Fibre and enteral nutrition

The recent launch of a number of fibre enriched polymeric diet in the United States and Europe has stimulated considerable interest in the topic of fibre and enteral nutrition, and several commercial concerns appear to be under considerable pressures from their consumers to produce similar products. As a means of identifying areas of potential application of fibre to enteral nutrition some of the recent knowledge gained about the physical properties of dietary fibre and the processes involved in the intestinal assimilation of fibre has been reviewed. Two areas of interest are identifiable. The first relates to the bulking properties of fibre and the application of this to the regulation of bowel function in enterally fed patients. It is clear from the clinical studies that have been reviewed that there remains a paucity of controlled data, and a great deal more research is needed before widespread use of fibre supplemented diets can be supported. Perhaps of greater interest academically is the potentially beneficial effects that appear to be exerted by the VFA's, liberated as a consequence of colonic bacterial fermentation of fibre, on morphology and function of ileal and colonic mucosa. Although there are a number of potential applications of fibre supplemented enteral diets in this area, more research is required before any firm recommendations can be made about recommending their use. The one exception concerns patients with the nutritionally inadequate short bowel syndrome. There does seem to be sufficient experimental evidence to suggest that clinical studies should be commenced using a pectin supplemented predigested 'elemental' diet in these patients. Overall therefore, one is forced to conclude that the increasing interest and use of fibre supplemented enteral diets is being driven more by market than scientific forces. Nevertheless, the promotion of these diets has already provided a powerful stimulus to the scientific community, and it remains entirely possible that many of the potential applications of these diets will be realised in the near future.

Impact of long-term relative bowel rest on conditions for colonic surgery

Collagen content, bursting wall tension, and suture-holding capacity in the proximal and distal colon of the rat were studied after long-term treatment with a low-residue or a standard laboratory chow diet. Collagen content decreased uniformly in both the proximal and distal colon of the low-residue diet group. In addition, the bursting wall tension of the nonoperated proximal colon was reduced, whereas the breaking strength of a newly constructed anastomosis at three different colonic sites was unaffected.

Effect of parenteral nutrition supplemented with short-chain fatty acids on adaptation to massive small bowel resection

After massive small bowel resection, total parenteral nutrition (TPN) is prescribed to maintain nutritional status. However, TPN reduces the mass of the remaining intestinal mucosa, whereas adaptation to small bowel resection is associated with increased mucosal mass. Short-chain fatty acids (SCFAs) have been shown to stimulate mucosal cell mitotic activity. This study determined whether the addition of SCFAs to TPN following small bowel resection would prevent intestinal mucosal atrophy produced by TPN. Adult rats underwent an 80% small bowel resection and then received either standard TPN or TPN supplemented with SCFAs (sodium acetate, propionate, and butyrate). After 1 wk, jejunal and ileal mucosal weights, deoxyribonucleic acid, ribonucleic acid, and protein contents were measured and compared with the parameters obtained at the time of resection. Animals receiving TPN showed significant loss of jejunal mucosal weight, deoxyribonucleic acid, ribonucleic acid, and protein and ileal mucosal weight and deoxyribonucleic acid after small bowel resection, whereas animals receiving SCFA-supplemented TPN showed no significant change in the jejunal mucosal parameters and a significant increase in ileal mucosal protein. These data demonstrate that SCFA-supplemented TPN reduces the mucosal atrophy associated with TPN after massive bowel resection and thys may facilitate adaptation to small bowel resection.

The role of the liver in the protection by elemental diets against experimental colon cancer

This study investigates the mechanism whereby the elemental diet 'Vivonex' protects against experimental colon cancer. A total of 240 Wistar rats were randomly allocated to three dietary groups: (A) Vivonex HN, (B) Vivonex HN with 0.05% added cholesterol and (C) control standard powdered diet. All received a colon cancer-producing regimen of dimethylhydrazine (DMH) at a dose of 40 mg/kg BW, s.c., once weekly for 5 weeks. Ten weeks following the first DMH injection, then at 5 weekly intervals until the 40th week, 10 randomly selected rats from each dietary group were weighed, killed and necropsied. Total liver weights were recorded with samples kept for total lipid extraction and cholesterol and phospholipid assay. Each colon underwent macroscopic examination and all neoplasms were recorded. Results showed that control rats had a constant total liver lipid content over the 40 weeks and an increased incidence, number and development of colonic neoplasms with time. In contrast, Vivonex fed rats had significantly elevated total liver lipids, cholesterol and phospholipids over the 40 weeks compared to controls and a significantly reduced number and rate of development of colonic neoplasms. Rats fed on Vivonex + cholesterol had total liver lipids intermediate and significantly different from both the Vivonex and control groups and a similar result was seen in tumour development with time. This study shows that a Vivonex diet results in an increase in hepatic lipids, this effect being partially reversed with dietary cholesterol. The protective effect of Vivonex feeding in the DMH model of colon cancer may thus be mediated in part by the liver.(ABSTRACT TRUNCATED AT 250 WORDS)